The research program described here is designed to study the immunopathological and oncological consequences of endogenous retroviral gene expression. Basically, these studies represent a continuation of the efforts of a research team which has been functioning together on this project for eight years. The basic concept which draws the research efforts together is the realization that many host factors determine the outcome of endogenous retroviral gene expression and to approach a final understanding of how these viruses cause disease requires cooperation between investigators studying the molecular nature of the genes per se as well as those who understand how host defense systems impinge upon viral replication and viral gene expression in the absence of viral replication. Thus, within the confines of this program project we will study: a) the nature of the genes and gene products which give rise to leukemogenic transformation, b) the mechanism by which the complement cascade recognizes and lyses retroviruses, c) the immunopathological consequences of endogenous retroviral gene expression with particular emphasis on immune complex disease.